BEIJING (Reuters) – China extended monthly air quality rankings to 169 cities from 74, including in the high-pollution region of Shanxi-Shaanxi in the country’s northwest, adding pressure on local authorities as it intensifies its campaign against air pollution.

Cities in the Fenwei plains area of Shanxi, Shaanxi and Henan provinces, the Sichuan-Chongqing region and middle reaches of the Yangtze River were added to the previous rankings, which had focused mainly on 28 northern cities and provincial capitals known for their smog-filled skies.

“By including more cities in the ranking, it will strengthen public supervision on air pollution and urge local governments to adopt effective measures to improve air quality,” said the Ministry of Ecology and Environment (MEE) in a statement on Monday.

The country earlier this month expanded its anti-pollution fight to 82 cities across China in a long-awaited 2018-2020 pollution action plan published earlier this month.

The ranking system is part of an effort included in the anti-pollution action plan to pass pollution-control pressure over to local governments.

The MEE also said as part of the ranking that every month it will publish the 20 cities with the best air quality and the 20 cities with the worst pollution across the country.

Tangshan, top steelmaking city in Hebei province, was named as the worst place for air quality in the new list of 169 cities in June, according to the MEE. Coal-producing hub Linfen performed worst for the first half of the year.

Capital Beijing also appeared as one of the 20 worst offenders for air pollution in June, with its concentration of small particulate matter (PM2.5) jumping 14.3 percent from a year ago. This is the second month in a row for Beijing to be found as one of the nation’s most polluted cities.

On Friday, Tangshan started six weeks of production curbs at steel mills, coke producers and coal-fired power plants to deepen reductions in toxic emissions.

Average PM2.5 concentrations in 338 prefecture-level cities that are closely monitored by the central government were at 44 microgram per cubic meter in January-June this year, down 8.3 percent from same period last year but still above the national target of 35 micrograms per cubic meter.